1. Field of the Invention
This invention relates to a magnetic eraser device for erasing records on magnetic recording media, and more particularly to a magnetic eraser device having a plurality of erase heads arranged in juxtaposition.
2. Description of the Prior Art
Cassette tapes have a narrower tape width than that of those tapes commonly used with open reels, and accordingly a narrower track width than that of the latter tapes.
A cassette tape, as shown in FIG. 1 of the accompanying drawings, has a tape width of 3.81 mm, and in case of the monaural system, two recording tracks each having a width of 1.5 mm are provided in parallel spaced relationship on such tape with a blank section of 0.8 mm width interposed therebetween, in the manner as shown in FIG. 1A. In case of the stereophonic system, two left and right tracks for recording stereophonic signals are formed in each monaural track to assure the compatibility with the monaural system. For example, as shown in FIG. 1B, two recording tracks each having a width of 0.6 mm are provided in each monaural track with a blank section of 0.3 mm width interposed therebetween.
A magnetic eraser device as indicated by 11 in FIG. 1A has heretofore been used with such cassette tape having monaural tracks formed therein. The magnetic eraser device 11 comprises an erase head 13 having a gap length substantially equal to the width of a recording track 12 on the cassette tape 10, the erase head 13 being disposed so as to correspond to the track 12. An erase current applied to such erase head 13 may erase the record on the track 12, whereafter any desired new information may be recorded on the erased track by means of a recording head 15 forming a magnetic recording device 14.
Turning to FIG. 1B, a magnetic eraser device 16 usable with a tape having stereophonic tracks may likewise comprise a magnetic erase head 17 having an erase gap length similar to that in the aforesaid monaural system the erase head 17 being used to erase the recording tracks in the right and left channels 18 and 19 at a time. Thereafter, two types of new information may be recorded on those erased tracks by means of two record heads 21 and 22 forming a magnetic recording device 20.
Where the tape is thus used as an ordinary stereophonic tape, the use of a single erase head for erasing two tracks simultaneously as shown in FIG. 1B would encounter no problem. However, when it is desired to record distinct signals entirely discretely on the respective tracks 18 and 19 which form stereophonic tracks, the stereophonic tracks 18 or 19 must be erased individually.
For example, where the stereophonic cassette tape as shown in FIG. 1B is used for the foreign language training, the instructor's model pronounciation is prerecorded on one of the tracks such as 18 and the trainee may play back this track to reproduce and listen to the instructor's pronounciation as he erases the other track 19 while speaking after the instructor's model pronounciation to thereby have the signals representative of his own pronounciation recorded on the erased track, whereafter the trainee may play back both tracks to listen to the signals reproduced from the two tracks, thus aurally comparing his own pronounciation with the instructor's model to check up any defects or differences in his own pronounciation.
Thus, in such language training applications, the content of the track 18 must not be erased while the track 19 alone must be erased. For such purposes, the magnetic eraser devices as shown in FIG. 2 have been widely used. One of them, as shown in FIG. 2A, comprises erase heads 23 and 24 corresponding to the two tracks 18 and 19 and each having a gap length substantially equal to the width of each track, the erase heads 23 and 24 being shown with their respective gaps 25 and 26 being substantially aligned with each other. Such aligned head gaps, however, might result in a possibility that even when one of the erase heads such as 24 is being operative to erase only one of the tracks such as 19, some leakage flux which may usually present around the head gap 26 reaches the erase head 23 to provide an erase flux between the magnetic heads 23 and 24 and between the head gaps 25 and 26 which would adversely affect the signals recorded on the track 18.
To eliminate such a drawback, there will occur to mind an arrangement as shown in FIG. 2B wherein erase heads 27 and 28 corresponding to the two tracks 18 and 19 have their head gaps 29 and 30 located in offset relationship with each other. Nevertheless, both of the magnetic eraser devices as shown in FIGS. 2A and B would encounter difficulties if they are used with a monaural tape. Even if the two heads such as 23 and 24 or 27 and 28 are simultaneously energized to erase one track such as 12 in the monaural tape, the flux density between the two erase heads will necessarily become decreased to leave the recorded signals unerased. If the two adjacent erase heads are brought into closer proximity in order to eliminate such unerased signals which result during the monaural mode, there would occur another inconvenience that when only one of the tracks is to be erased in order to have signals recorded discretely on the stereophonic tracks, part of the other track is also erased out. It will thus be apparent that the extent of proximity permissible between the two heads is necessarily limited and that even the maximum proximity within such limit will not be successful in erasing the monaural track.
A magnetic eraser arrangement for proving such compatibility with the monaural system is shown in FIG. 2C, wherein there is provided an erase head 31 corresponding to one of the stereophonic tracks such as 19 and an erase head 32 adjacent to the head 31 and corresponding to the monaural track. In the magnetic eraser device as shown in FIG. 2C, the magnetic head 31 is energized to erase one of the stereophonic tracks (e.g., track 19) and the magnetic head 32 is used to erase the two tracks or the monaural track. Such arrangement of the erase heads ensures the compatibility between the monaural and the stereophonic system, but unfortunately increases the size of the magnetic eraser device. Moreover, this arrangement cannot erase the track 18 independently of the other track and if an additional erase head were provided to erase the track 18 alone, the magnetic eraser device would become much larger in size.